Google Voice provides a voicemail feature with
a useful (if often comically inaccurate) transcription feature. The way in
which one normally enables this feature is to dial a series of digits which
instructs the cell provider to forward missed calls to an alternate number.
However, for Ting this is not supported, at least not on
all devices.

The workaround is simple, though not widely advertised; forwarding must be
configured from the Ting Dashboard. The steps to do this
are as follows:

In the "Minutes" section, check the Forward 'busy signal' calls to this
number and Forward 'no answer' calls to this number checkboxes, and
enter your Google Voice number in both corresponding input boxes.

I also unchecked the Voicemail box since I wasn't going to be using
Ting voicemail, but this is probably not necessary.